This invention relates to nozzles for the continuous casting of lead strip, and more particularly to means for cooling same with coolants (e.g., water) which are readily vaporizable at the melting point of the lead.
In the continuous casting of lead strip a lead melt is introduced into the inlet of a casting nozzle having a chilled surface therein defining a mold cavity therethrough for solidifying the melt. The casting nozzle is thermally isolated from the melt source by a refractory material and melt passing through the refractory begins to solidify as a thin skin at the inlet of the chilled nozzle, which skin grows inwardly as the metal progresses through the nozzle and finally immerges the nozzle as a solidified strip. The inlet of the cavity adjacent the refractory is one of the most critical regions of the nozzle as it is the locus of the formation of the initial solid skin which permits pulling of the strip from the nozzle. The strength of the skin at the inlet plays a significant role in the rate at which the strip can be cast which in turn is a function of the metallurgical properties (e.g., tensile strength, etc.) of the metal itself and the thickness of the skin at the inlet. The combination of metallurgical properties and thickness of the skin at the inlet determines the amount of pull the skin can withstand before rupturing. Skin rupture can cause the melt source to become "unplugged" and dump through the nozzle or otherwise create unacceptable defects on the cast strip. In the case of metallurgically weak metals such as lead or its alloys (hereafter lead), skin strength at the inlet is achieved primarily by thickness, and thickness is achieved by maximum heat removal at the inlet of the nozzle. The inlet, however, is also the hottest part of the nozzle and hence tends to vaporize preferred coolants such as water in the cooling channels, and with the formation of insulating vapor films in the cooling channels circumscribing the inlet the heat removal rate is substantially diminished.
It is therefore an object of the present invention to provide an improved cooling arrangement for casting nozzles which maximizes the effectiveness of the coolant in the total solidification process, but primarily in the region of the nozzle inlet where the invention insures that coolant flows in a turbulent, vapor-film-purging manner in the cooling channel circumscribing the inlet.
This and other objects and advantages of the invention will become more readily apparent from the description which follows and particularly as it relates to FIGS. 3 and 4 hereof.